1. Field of the Invention
This invention relates to a safety apparatus for a construction equipment such as a crane including a revolvable upper revolving member such as a boom which sets a rated load in accordance with extended conditions of support members of the construction equipment and performs a safety operation such as compulsory stopping of driving of the upper revolving member or alarming in accordance with the rated load.
2. Description of the Prior Art
Generally, in construction equipments of the type mentioned, it is important to prevent buckling, over turning and so forth during revolving operation, and to this end, various safety apparatus have been proposed wherein operation of an upper revolving member such as a boom is automatically stopped when the operating condition of the upper revolving member comes out of a safety region.
In conventional safety apparatus, an allowance requirement is set equally over the entire range of 360.degree. irrespective of a revolving angle of the upper revolving member around its axis. However, since extendible support members such as outrigger jacks provided on a crane cannot always be extended completely horizontally and the horizontally extended amounts of the support members may be partially different depending upon an operating site such as a narrow road, the allowance requirement must necessarily be changed also depending upon the revolving angle of the upper revolving member.
A safety apparatus is disclosed in Japanese Patent Laid-Open Application No. 57-27893 wherein an operating condition of a crane is detected every moment and a rated load of the crane is decided from the detection value and preset values of the lifting capacity stored for various conditions, and then a safety operation is performed in accordance with a result of comparison between the rated load and an actual load.
Another safety apparatus is disclosed in Japanese Patent Laid-Open Application No. 3-115091 wherein a critical operating region of a boom is set in accordance with a horizontal extension amount of each support member and a safety operation is controlled in accordance with the critical operating region. The critical operating region may be set such that, where the horizontal extension amounts of the left and right support members are different from each other, a stable section and an unstable section are determined with regard to a revolving direction of the boom, and a first operating radius is set for the stable section while a second operating radius smaller than the first operating radius is set for a most unstable section within the unstable section and the operating radius is decreased continuously from the first operating radius to the second operating radius for any other section within the unstable section.
Since the apparatus disclosed in Japanese Patent Laid-Open Application No. 57-27893 calculates a rated load every moment in accordance with extended conditions of the outrigger jacks at present, a curve (rated load curve) which is obtained by interconnecting the rated loads at the various revolving angles calculated by the apparatus presents an irregular profile, and consequently, there is a disadvantage that it is difficult for the operator to grasp the curve. For example, in case the boom is revolved in a condition wherein the operating radius is fixed, the rated load is sometimes decreased suddenly even by a small change of the revolving angle, and the operator cannot forecast a variation of the rated load by revolving movement at all. Accordingly, very careful operation is required for the operator.
On the other hand, with the apparatus disclosed in Japanese Patent Laid-Open Application No. 3-115091, since an allowable operating radius is calculated from a hoisting load to the upper revolving member and an allowable operating range is set in accordance with the allowable operating radius, a critical operating region can be grasped comparatively readily. However, generally in a construction equipment such as a crane, it is strongly demanded to effect, for the purpose of safely, a safety operation (alarming, compulsory stopping, displaying of a load factor or the like) based on a load factor (ratio of the hoisting load to the rated load), and such safety operation is already carried out widely and commonly. In order to calculate a critical operating region with the apparatus described above, the relationship between an operating radius and a revolving angle when the hoisting load at present is equal to the rated load must be calculated, quite separately from the calculation of a load factor, every time from data of the rated load corresponding to extension amounts of the support members and/or an operating radius of the upper revolving member. Thus, there is a disadvantage that the calculating apparatus is complicated as much and the necessary capacity is increased as much.
It is to be noted that, while an apparatus is proposed in Japanese Patent Laid-Open Application No. 3-73795 wherein a load factor is calculated over the entire circumference of an upper revolving member and is displayed as a load factor image, what calculation of a load factor is performed concretely in accordance with an operating posture of a crane is not disclosed in the prior art document. Accordingly, the apparatus does not make a solution to the subject described above.